1. Field of the Invention
The present invention relates to an ink-jet printing head, more particularly relates to a method of producing a flow passage forming substrate.
2. Description of the Related Art
In an ink-jet printing head, as shown in FIG. 13, a flow passage unit is constituted by a flow passage forming substrate F in which a reservoir A to which ink is supplied from an outside tank, a pressure generating chamber B which is concave and pressurized from the outside, an ink supply port C connecting the reservoir A and the pressure generating chamber B and a nozzle communicating hole E which is a through hole and connects the pressure generating chamber B and a nozzle aperture D are formed, an elastic plate G for sealing one surface of the flow passage forming substrate F and a nozzle plate H provided with the nozzle aperture D for sealing the other surface of the flow passage forming substrate F. The ink-jet printing head is constituted so that ink in the reservoir A is sucked in the pressure generating chamber B via the ink supply port C by touching a piezoelectric vibrator J to the elastic plate G and expanding the pressure generating chamber B by the displacement of the piezoelectric vibrator J and an ink droplet ejects from the nozzle aperture D by pressurizing ink the pressure generating chamber B by contracting the pressure generating chamber B.
As in such an ink-jet printing head, full color printing can be readily executed by using color ink, the ink-jet printing head is rapidly popularized as a printing head of a color printer and hereby, it is demanded that printing quality and density are further enhanced.
As the printing quality and density of an ink-jet printing head greatly depend upon the size of a dot which an ink droplet forms, it is required to reduce the quantity of ink per droplet as much as possible to miniaturize the size of a dot.
Therefore, the volume of a pressure generating chamber can be reduced as much as possible and, in addition, pressure generating chambers can be arrayed in high density by arraying pressure generating chambers in high density, selecting a substrate 300 .mu.m or more thick, desirably a substrate approximately 500 .mu.m thick, for example a monocrystalline silicon substrate in view of working precision as a flow passage forming substrate in consideration of preventing a flow passage forming substrate from being deformed by pressure when an ink droplet ejects and, further, facility in handling in assembly and forming the pressure generating chamber as a shallow concave portion by photolithography and anisotropic etching as disclosed in Unexamined Japanese Patent Application No. Sho. 58-40509.
When the pressure generating chamber is constituted on one surface of the substrate as a concave portion as described above, the nozzle communicating hole E for connecting the pressure generating chamber and the nozzle aperture is required to let the pressure generating chamber communicate with the nozzle aperture D of the nozzle plate arranged on the surface on the side reverse to the surface on which the pressure generating chamber is formed.
Such a nozzle communicating hole E is formed by making a through hole with a minute diameter pierced from one surface to the other surface in an area to be the nozzle communicating hole E beforehand as disclosed in Unexamined Japanese Patent Application No. Sho. 5-309835 and executing anisotropic etching to the depth using the above through hole as an etching pilot hole so that the width of the nozzle communicating hole E is approximately equal to the width of the pressure generating chamber B at the maximum.
Therefore, as shown in FIG. 14, as the height of a partition in an area K' which faces the nozzle communicating hole E is equal to the thickness d' of the monocrystalline silicon substrate and large though the partition in the vicinity of the pressure generating chamber is provided with high rigidity because the depth d of the pressure generating chamber B is small in an area K in the vicinity of the pressure generating chamber of partitions for partitioning the pressure generating chambers B, the rigidity of the partition between the adjacent nozzle communicating holes E is extremely small and there is a problem that pressure when ink is jetted elastically deforms the area K' and crosstalk is caused between the adjacent pressure generating chambers B.